Mass spectrometric analysis of chromatographic results often fails to distinguish two or more components eluted with retention times so close that the total ion current trace appears as a single peak. This situation is common in the analysis of wastewater, hazardous waste, and organic tissue samples. Manual interpretation of such spectra is impossible, as even the most skilled operator is faced with a task that resembles that of finding the proverbial needle in a haystack. Library search programs are of limited utility for much the same reason.
A commonly used algorithm (termed Biller-Biemann, after its originators) provides a routine for the analysis of overlapping spectra components. (See Biller, J. Biemann, K. Anal Letters 1974, 7, 515). A spectrum is generated which incorporates mass/intensity pairs only from those mass to charge ratios which have mass chromatogram maxima at or adjacent to the selected scan. Thus, if two components have no common mass to charge ratios and they can be separated by two or more scans, distinct spectra can be generated for each component. Although this algorithm is simple to implement, the results are of limited utility due to insufficient resolution.
Arguably more powerful than Biller-Biemann is an algorithm suggested by Dromey (Dromey, R. G.; Stefik, M. J.; Rindfleisch, T. C.; Duffielk, A. M. Anal. Chem. 1976, 48, 1365) which bases the analysis of peaks on the concept that all peaks for a single component will have the same shape. However, commercial implementation of this algorithm has yet to be successful.
Alternatively, Colby, in "Spectral Deconvolution for Overlapping GC/MS Components" J Am Soc Mass Spectrom 1992, 3,558-562, reports a deconvolution algorithm which attempts to extend the Biller-Biemann algorithm to allow assessment of peak shape yet retain simplicity sufficient for commercial applications. However, none of the methods reported to date finds all possible components in a data file, thoroughly deconvolutes spectra, or functions automatically. It is clear from the foregoing that a simple, effective, and automatized means for distinguishing between closely eluted analytes in GC/MS analysis is much needed.